linux-kernel - Re: start_kernel(): bug: interrupts were enabled early

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Message-Id: <20100331182654.d36c87ff.akpm@linux-foundation.org>
Date:	Wed, 31 Mar 2010 18:26:54 -0400
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Matthew Wilcox <matthew@....cx>,
	Yinghai Lu <yinghai@...nel.org>, Rabin Vincent <rabin@....in>,
	lkml <linux-kernel@...r.kernel.org>, penberg@...helsinki.fi,
	linux-arch@...r.kernel.org
Subject: Re: start_kernel(): bug: interrupts were enabled early

On Thu, 01 Apr 2010 12:17:11 +1100 Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:

> On Wed, 2010-03-31 at 15:49 -0700, Andrew Morton wrote:
> > 
> > But these things are all utterly gross.  The bottom line is that
> > radix_tree_init() is manifestly unsuited to being called with local
> > interrupts disabled.  773e3eb7b81e5ba13b5155dfb3bb75b8ce37f8f9 was
> > just a wrong patch. 
> 
> Except that powerpc (and now it seems x86) both want to use radix trees
> for interrupt handling... At least on powerpc, we trick and use a linear
> search until the radix trees are initialized, which we do later during
> boot, but that somewhat sucks.
> 
> I believe sherry picking things like not calling radix_tree_init() is
> going to fix one case today, until we have another one, and another one,
> and etc...
> 
> I suspect we're better off fixing the root of the problem in down/up.
> 

Not by adding overhead to every single down_read()/down_write() just to
fix a once-off startup problem - that's taking laziness way too far.

We'd be better off hacking a kmem_cache_create() special case to avoid
taking the rwsem.  Add SLAB_I_SUCK to `flags' perhaps.

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